An electroluminescent (EL) lamp generally includes a layer of phosphor positioned between two electrodes, and at least one of the electrodes is light-transmissive. At least one dielectric also is positioned between the electrodes so the EL lamp functions essentially as a capacitor. When a voltage is applied across the electrodes, the phosphor material is activated and emits a light. EL lamps typically are manufactured as discrete cells on either rigid or flexible substrates. One known method of fabricating an El, lamp includes the steps of applying a coating of light-transmissive conductive material, such as indium tin oxide, to a rear surface of polyester film, applying a phosphor layer to the conductive material, applying at least one dielectric layer to the phosphor layer, applying a rear electrode to the dielectric layer, and applying an insulating layer to the rear electrode. The various layers; may, for example, be laminated together utilizing heat and pressure. Alternatively, the various layers may be screen printed to each other. When a voltage is applied across the indium tin oxide and the rear electrode, the phosphor material is activated and emits a light which is visible through the polyester film.
Typically, it is not desirable for the entire EL polyester film to be light emitting. For example, if an EL lamp is configured to display a word, it is desirable for only the portions of the EL polyester film corresponding to letters in the word to be light emitting. Accordingly, the indium tin oxide is applied to the polyester film so that only the desired portions of the film will emit light. For example, the entire polyester film may be coated with indium in oxide, and portions of the indium tin oxide may then be removed with an acid etch to leave behind discrete areas of illumination. Alternatively, an opaque ink may be printed on a front surface of the polyester film to prevent light from being emitted through then entire front surface of the film.
Fabricated EL lamps often are affixed to products, e.g., signs, and watches, to provide lighting for such products. For example, EL lamps typically are utilized to provide illuminated images on display signs. Particularly, and with respect to a display sign, EL lamps are bonded to the front surface of the display sign so that the light emitted by the phosphor layers of such lamps may be viewed from a position in front of the sign.
Utilizing prefabricated EL lamps to form an illuminated display sign is tedious. Particularly, each EL lamp must be formed as a reverse image. For example, when utilizing an EL lamp to display an illuminated word, e.g., "THE", it is important that the word be accurate, i.e., be readable from left to right, when viewed from the front of the sign. Accordingly, and until now, it was necessary to apply the indium tin oxide to the polyester film as a reverse image, e.g., as a reverse image of "THE". The subsequent layers of phosphor, dielectric, and rear electrode then are similarly applied as reverse images. In addition, it is possible that the EL lamp may become damaged while bonding the EL lamp to the sign.
Accordingly, it would be desirable to provide a method for fabricating an illuminated sign having EL lamps which does not require coupling prefabricated EL lamps to the sign. It also would be desirable for such method to facilitate applying the various layers of the EL Limps to the EL substrate as a forward image, rather than a reverse image.